How does rolls and chance work in distribution?

[local306]

I'm making some modded items that I want zombies to occasionally have in their inventory when killed.

 

I found some posts that got me started for adding said items into inventorymale and inventoryfemale loot tables. 

 

My issue is that there are too many of my items spawning per corpse. My rolls are set to 1 and my chances are set to values well below 1. However dead zombies sometimes have 3 or more items per corpse, and manually checking the collected item distribution is nowhere near what I set their chance distribution to be. 

 

Someone on Discord said that each item that I have added to zombie loot tables has 1 chance to roll which explains the multiple items showing up (unique per roll). Why doesn't it seem to abide by my chance values though? Like one item is set to 0.0001 for testing and it was the second most found item after kill 500 zombies.

 

Basically how to I actually get really rare drops from the items I'm adding? I have about 50 items I'm adding and they are WAY to common with my current settings.